The present invention relates to an intermodulation signal detector for use in a non-linear super high frequency circuit for stably detecting an intermodulation signal by using two transmission lines having the same amplitudes and different phases.
In general, if a super high frequency circuit having a non-linear characteristic receives signals having different frequencies, a new frequency signal is produced by an interaction of the received signals. Such a produced signal is called an intermodulation signal. The intermodulation signal is different from a converted signal of the received signal, which is generated by linear transmission operation of the super high frequency circuit. The intermodulation signal is produced from inside of the super high frequency circuit and acts as a noise disturbing the received signals. Therefore, the intermodulation signal diminishes an ability of transmitting information of a circuit.
A power amplifier generally produces a plenty of intermodulation signals due to power efficiency and non-linearity of amplifying devices.
A conventional intermodulation signal detector detects intermodulation signals by applying a power divider behind a transmission line, producing a control signal by using a frequency mixer and a frequency converter through a controller and controlling a variable attenuator and a variable phase converter, which are located in front of a power amplifier, in response to the control signal.
The above-mentioned conventional intermodulation signal detector is characterized as a controllable detector by the control signal of the controller.
FIG. 1 is a block diagram of a conventional intermodulation signal detector of a super high frequency circuit having non-linear characteristics. The conventional intermodulation signal detector uses a microprocessor as a controller for detecting an intermodulation signal.
The conventional intermodulation signal detector includes power dividers 120, 124 and 126, a variable attenuator 121, a variable phase converter 122, a non-linear super high frequency element 123, a subtracter 125, a frequency mixer 127, a receiver 128, a controller 129, a voltage control frequency generator 130 and transmission lines 101 to 116.
The power divider 120 receives an output signal of the transmission line 101 and distributes the power of the received signal to the reference transmission line 107 and the circuit transmission line 102.
The power distributed to the super high frequency circuit transmission line 102 is applied to the variable attenuator 121 and the variable phase converter 122, which are controlled by a voltage outputted from the controller 129.
The power transferred through the variable attenuator 121 and the variable phase converter 122 is applied to the non-linear super high frequency element 123 through the super high frequency transmission line 103. The non-linear super high frequency element 123 outputs the applied power together with an intermodulation signal through the transmission line 104 to the power divider 124, wherein the intermodulation signal is generated in the non-linear super high frequency element 123. The power divider 124 outputs the applied power and the intermodulation signal to the outside through the transmission line 105 and to the subtracter 125 through the transmission line 106.
The subtracter 125 compares a reference signal with the signal provided from the power divider 124, wherein the reference signal is the power transmitted from the power divider 120 through the transmission line 107. After performing the comparison process, the subtracter 125 subtracts the signal transmitted from the power divider 124 from the reference signal and outputs a subtracted signal to the power divider 126 through the super high frequency transmission line 108. Herein, the subtracted signal is the intermodulation signal. The power divider 126 provides the intermodulation signal to the outside through the super high frequency transmission line 109 and to the frequency mixer 127 through the super high frequency transmission line 110.
The frequency mixer 127 receives the intermodulation signal provided from the power divider 126 and a signal outputted from the voltage control frequency generator 230, mixes frequencies of the received signals and provides a mixed frequency signal to the controller 129 through the receiver 128.
In response to the mixed frequency signal inputted thereto through the receiver 128, the controller 129 controls the variable attenuator 121 and the variable phase converter 122 by using the control transmission line 115 and 116, respectively, to thereby output a signal having the same power amplitude and 180xc2x0 reversed phase with the reference signal on the reference transmission line 107 to the subtracter 125 through the transmission line 106.
As a result, the subtracter 125 can output the subtracted signal only composed of the intermodulation signal.
In the meantime, since the conventional intermodulation signal detector uses a microprocessor as the controller 129, it is difficult to process data in real-time. Additionally, it is also difficult to stably detect the intermodulation signal regardless of variations of the non-linear characteristics of the super high frequency circuit and an external environment.
It is, therefore, a primary object of the present invention to provide an intermodulation signal detector of a non-linear super high frequency circuit for detecting in real-time an intermodulation signal generated at a super high frequency element having a non-linear characteristic.
Another object of the present invention is to provide an intermodulation signal detector of a non-linear super high frequency circuit for stably detecting intermodulation signals regardless of variations of non-linear characteristics of the super high frequency element and an external environment.
In accordance with an aspect of the present invention, there is provided an intermodulation signal detector for use in a super high frequency circuit, including: a first power dividing unit for dividing the power of a super high frequency signal inputted from the outside through a super high frequency transmission line, and outputting a power-divided signal; a clock generating unit for providing a clock signal; a varying unit for receiving the power-divided signal from the first power dividing unit, attenuating an amplitude of the power-divided signal according to an amplitude control signal, converting a phase of the power-divided signal in response to a phase control signal and providing a converted super high frequency signal having converted amplitude and phase; a non-linear super high frequency element for receiving the converted super high frequency signal and generating an output signal including the converted super high frequency signal and an intermodulation signal produced therein; a second power dividing unit for receiving the output signal of the non-linear super high frequency element, dividing the power of the output signal and outputting a power-divided output signal as a comparison signal; a third power dividing unit for receiving the power-divided signal from the first power dividing unit and dividing the power of the power-divided signal twice power-divided signal as a reference signal; a power combining unit for receiving the comparison signal and the reference signal and combining the received two signals to thereby detect the intermodulation signal; a phase control unit for receiving the comparison signal and the reference signal and generating DC voltages having a amplitude corresponding to the phases of the two signals to thereby produce the phase control signal for making of the phase difference between the comparison signal the reference signal 180xc2x0; and an amplitude control unit for receiving the comparison signal and the reference signal and generating DC voltages having a amplitude corresponding to the amplitudes of the two signals to thereby produce the amplitude signal for making the amplitude of the comparison signal identical to that of the reference signal.